Character creation can be done either via character sheeting – the
easiest way to twink for veteran RPG fans – or by following quests in
the first hour of the Vault, as the main character advances from birth
to age nineteen.

On the AI:

Enemies are incredibly intelligent in Fallout 3. Very early on, we saw
a super mutant attempt to flank Todd Howard’s character, though the
super-statistics of his demo character allowed him to easily take down
the underground foe.